I'm a 5K runner and during the last 1/3 of the race it's always a battle against my stomach. It feels like it cramps up, starts hurting/burning, and it's tough to run through it. It happens almost every time I race. I eat light the morning before races, usually a piece of toast or two + water/gatorade, and sometimes I'll have a small cup of coffee to get me going / help take a dump before the race. Does anyone else struggle with this?